The Vietnamese Communists employed thousands of mines
against U.S. and allied naval forces throughout the conflict in Vietnam,
much as they had against the French during the First Indochina War. Between
1959 and 1964, Viet Cong mines, often homemade devices, took an increasing
toll of naval vessels and civilian craft on the many rivers and canals of
South Vietnam. This threat ended commercial traffic on some of the country's
primary waterways.

As U.S. naval forces deployed to South Vietnam in the mid-1960s, moving into
the watery environment of the Mekong Delta west and south of Saigon, they
took steps to counter the enemy's mine threat. The danger was especially
acute on the waterways near Saigon, South Vietnam's most important port.
Viet Cong closure of the Long Tau River, which followed a meandering,
forty-five-mile course through the Rung Sat swamp on its way to the capital,
would have put an enormous strain on allied logistic resources in the
southern regions of South Vietnam.

As a result, on 20 May 1966 the Navy established
Mine Squadron 11, Detachment Alpha (Mine Division 112 after May
1968) at Nha Be. The minesweeping detachment operated 12 or 13 57-foot,
fiberglass-hulled minesweeping boats (MSB). The MSBs fought with machine
guns and grenade launchers and carried surface radars and minesweeping gear
for clearing explosives from the rivers. The Navy also set up three-boat
sections at Danang and Cam Ranh Bay. Detachment Alpha's strength increased
in July 1967 when the first of six mechanized landing craft, minesweeping (LCM(M))
reached Nha Be.

Despite the presence on the Long Tau of Mine
Squadron 11 and other river warfare forces, in the second half of
1966 and early 1967 the Communists mounted a serious effort to interdict the
waterway. The Viet Cong employed mines, 122-millimeter rockets,
rocket-propelled grenades, recoilless rifles, machine guns, and small arms
against American and Vietnamese naval forces and merchantmen. In August
1966, Viet Cong mines severely damaged SS Baton Rouge Victory, a Vietnamese
Navy vessel, and MSB 54. Then that November, the enemy sank MSB 54. In
February 1967, Communist direct-fire weapons and mines destroyed MSB 45 and
heavily damaged MSB 49.

By the spring of 1967, however, the tide began to turn. Allied naval units
moved in force into the Rung Sat area, refined their mine countermeasures
tactics, and brought better weapons and equipment into play against the
enemy sappers. Vietnamese Regional Force, U.S. Army 9th Division troops, and
Navy SEAL commandoes, working with helicopter, river patrol boat, MSB, and
LCM(M)) units, scoured the shorelines. During the next year, Communist
guerrillas periodically ambushed ships on the Long Tau, but the fast and
devastating reaction by allied forces kept casualties and damage to vessels
relatively light. Often, the minesweeping force swept up mines before they
could do damage or river patrol boat and SEAL patrols disrupted enemy attack
plans. The upshot was that the Viet Cong were unable to cut or even
seriously slow logistic traffic on the Long Tau, even when their comrades
were fighting for their lives in Saigon during the Tet Offensive of early
1968.

During 1968 and 1969, the Navy also deployed strong mine countermeasures
forces to the Cua Viet River, just south of the Demilitarized Zone, and
defeated the North Vietnamese Army's attempt to cut the vital waterway.

Sources:

Marolda, Edward J. By Sea, Air, and Land: An Illustrated History of the U.S.
Navy and the War in Southeast Asia. Washington: Naval Historical Center,
1994.

Schreadley, Richard L. From the Rivers to the Sea: The U.S. Navy in Vietnam.
Annapolis: Naval Institute Press, 1992.